java@EJB返回null

1 周，3 日 Questions & Answers 8539

我是JBoss和J2EE的新手。我正在尝试用会话Bean联系单例Bean。长期来看，我想在Singleton bean中缓存一些信息，如果不可用，则在数据库中查找相关信息。但首先，我要创建最简单的用例

然而，当我在Eclipse中运行这个简单的用例（获取一个应用程序计数器）时，我得到了一个对EJB的空引用，我不确定下一步该转到哪里

我在运行Eclipse Keplar JDK1。7、JBoss AS 7.1、EJB 3.1

这是jsp文件

<?xml version="1.0" encoding="ISO-8859-1" ?>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<jsp:useBean id="counter" class="com.bender.counter.Counter" scope="session"/>
<%-- <jsp:useBean id="counterBean" class="com.bender.counterbean.CounterBean" scope="application"/> --%>

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>Test Counter</title>
</head>

<body>
Hit Counter( <%=counter.getHitCount() %> )<br/>
<%-- Hit CounterBean( <%=counterBean.getHits() %> )<br/> --%>
</body>
</html>

这里是第一个会话bean

package com.bender.counter;

import com.bender.counterbean.CounterBean;
import javax.ejb.EJB;
import javax.enterprise.context.SessionScoped;

@SessionScoped
public class Counter {
    @EJB 
    CounterBean counterBean;

    private int hitCount;

    public Counter() {
        this.hitCount = 0;
    }

    public int getHitCount() {
        if (counterBean == null) {
            System.out.println("Failure");
            hitCount = -1;
        } else {
            hitCount = counterBean.getHits();
        }
        return hitCount;
    }

    public void setHitCount(int newHits) {
        this.hitCount = newHits;
    }
}

这是单身豆

package com.bender.counterbean;

import javax.annotation.PostConstruct;
import javax.ejb.Singleton;
import javax.ejb.Startup;

@Startup
@Singleton
public class CounterBean {
    private int hits = 1;

    public CounterBean() {
        super();
        System.out.println("In constructor of CounterBean.");
    }

    @PostConstruct
    public void init(){
        System.out.format("In post Construct of CounterBean, hits( %d )%n", this.hits);
    }

    // Increment and return the number of hits
    public int getHits() {
        return hits++;
    }
}

这是服务器的输出。日志请注意，counterbean似乎向jndi注册。还请注意，jsp中的注释已被删除。这是试图从jsp联系CounterBean。那次尝试是成功的，所以我认为CounterBean在服务器上成功运行

17:07:50,427 INFO  [org.jboss.as.server.deployment] (MSC service thread 1-12) JBAS015876: Starting deployment of "Counter.war"
17:07:50,443 INFO  [org.jboss.as.ejb3.deployment.processors.EjbJndiBindingsDeploymentUnitProcessor] (MSC service thread 1-15) JNDI bindings for session bean named CounterBean in deployment unit deployment "Counter.war" are as follows:

    java:global/Counter/CounterBean!com.bender.counterbean.CounterBean
    java:app/Counter/CounterBean!com.bender.counterbean.CounterBean
    java:module/CounterBean!com.bender.counterbean.CounterBean
    java:global/Counter/CounterBean
    java:app/Counter/CounterBean
    java:module/CounterBean

17:07:50,458 INFO  [stdout] (MSC service thread 1-8) In constructor of CounterBean.

17:07:50,458 INFO  [stdout] (MSC service thread 1-8) In post Construct of CounterBean, hits( 1 )

17:07:50,474 INFO  [org.jboss.web] (MSC service thread 1-4) JBAS018210: Registering web context: /Counter
17:07:50,489 INFO  [org.jboss.as.server] (management-handler-threads - 83) JBAS018559: Deployed "Counter.war"
17:07:55,185 INFO  [stdout] (http-localhost-127.0.0.1-8080-1) Failure

谢谢你的帮助

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共 (2) 个答案

# 1 楼答案

注入只在DI容器（在JBoss中是weld）知道对象的情况下起作用。这通常是因为容器本身创建了实例。还可以将现有对象传递给容器，让它注入所有依赖项

CDI注入JSP页面似乎在JBoss AS 7中不起作用：

也许你可以看看JSP的替代方案：

JSF:Short JSF tutorial
Servlets:Short CDI injection tutorial for Servlets

如果你无法切换到其他技术，那么你可能不得不自己注射。使用以下方法让CDI容器对给定对象执行所有注入：

public static <T> void programmaticInjection(Class<T> clazz, T injectionObject) throws NamingException {
    InitialContext initialContext = new InitialContext();
    Object lookup = initialContext.lookup("java:comp/BeanManager");
    BeanManager beanManager = (BeanManager) lookup;
    AnnotatedType<T> annotatedType = beanManager.createAnnotatedType(clazz);
    InjectionTarget<T> injectionTarget = beanManager.createInjectionTarget(annotatedType);
    CreationalContext<T> creationalContext = beanManager.createCreationalContext(null);
    injectionTarget.inject(injectionObject, creationalContext);
    creationalContext.release();
}

然后从JSP调用此方法：

<h3>Inject Test</h3>
          <%
                    MyBean myBean = new MyBean();
                    myBean.programmaticInjection(MyBean.class, myBean);
                    // now call a method on myBean that invokes the injected EJB
          %>
</body>
</html>

这里是一个简单的JSF bean，与您的类似：

@Named("myBean")
@SessionScoped
public class MyBean implements Serializable {
    private static final Logger logger = LoggerFactory.getLogger(MyBean.class);
    private static final long serialVersionUID = 1L;
    private long taskId;
    @EJB
    private MyEjb myEjb;

在调用programmaticInjection()之后，@EJB注释对象将被注入

# 2 楼答案

我可以通过添加JNDI查找来解决这个问题。我必须在JBoss AS 7.1实例中设置一些不正确的内容，这样一个bean就可以使用（默认）JNDI，而JSP页面可以（完全）访问JNDI。以下是更新（和清理）的代码

JSP

<?xml version="1.0" encoding="ISO-8859-1" ?>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<jsp:useBean id="counter" class="com.bender.counter.Counter" scope="session"/>

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>Test Counter</title>
</head>

<body>
Hit Counter( <%=counter.getHitCount() %> )<br/>
</body>
</html>

会话Bean（注意@EJB被注释掉了）包裹通讯。本德。柜台

import com.bender.counterbean.CounterBean;

import javax.ejb.EJB;
import javax.enterprise.context.SessionScoped;
import javax.naming.InitialContext;
import javax.naming.NamingException;

@SessionScoped
public class Counter {
//    @EJB
    private CounterBean counterBean;
    {
        try {
            counterBean = (CounterBean) new InitialContext().lookup("java:global/Counter/CounterBean");
        } catch (NamingException e) { 
            e.printStackTrace();
        }
    }

    private int hitCount;

    public Counter() {
        this.hitCount = 0;
    }

    public int getHitCount() {
        if (counterBean == null) {
            System.out.println("Failure");
            hitCount = -1;
        } else {
            hitCount = counterBean.getHits();
        }
        return hitCount;
    }

    public void setHitCount(int newHits) {
        this.hitCount = newHits;
    }
}

还有独生子豆

package com.bender.counterbean;

import javax.annotation.PostConstruct;
import javax.ejb.Singleton;
import javax.ejb.Startup;


@Startup
@Singleton
public class CounterBean {
    private int hits = 1;

    public CounterBean() {
        super();
        System.out.println("In constructor of CounterBean.");
    }

    @PostConstruct
    public void init(){
        System.out.format("In post Construct of CounterBean, hits( %d )%n", this.hits);
    }

    // Increment and return the number of hits
    public int getHits() {
        return hits++;
    }
}

这是JBoss控制台的输出

16:21:55,740 INFO  [org.jboss.as.server.deployment] (MSC service thread 1-12) JBAS015876: Starting deployment of "Counter.war"
16:21:55,888 INFO  [org.jboss.as.ejb3.deployment.processors.EjbJndiBindingsDeploymentUnitProcessor] (MSC service thread 1-1) JNDI bindings for session bean named CounterBean in deployment unit deployment "Counter.war" are as follows:

    java:global/Counter/CounterBean!com.bender.counterbean.CounterBean
    java:app/Counter/CounterBean!com.bender.counterbean.CounterBean
    java:module/CounterBean!com.bender.counterbean.CounterBean
    java:global/Counter/CounterBean
    java:app/Counter/CounterBean
    java:module/CounterBean

16:21:56,033 INFO  [stdout] (MSC service thread 1-7) In constructor of CounterBean.

16:21:56,033 INFO  [stdout] (MSC service thread 1-7) In post Construct of CounterBean, hits( 1 )

16:21:56,088 INFO  [org.jboss.web] (MSC service thread 1-15) JBAS018210: Registering web context: /Counter
16:21:56,093 INFO  [org.jboss.as] (MSC service thread 1-15) JBAS015874: JBoss AS 7.1.0.Final "Thunder" started in 2001ms - Started 185 of 258 services (72 services are passive or on-demand)
16:21:56,176 INFO  [org.jboss.as.server] (DeploymentScanner-threads - 2) JBAS018559: Deployed "Counter.war"
16:22:11,455 INFO  [stdout] (http-localhost-127.0.0.1-8080-1) In constructor of CounterBean.

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java@EJB返回null

共 (2) 个答案

# 1 楼答案

# 2 楼答案